When a subject to be processed is drilled by applying laser beams, pulse irradiation of laser is performed many times on a subject to be processed, or processing is performed by irradiation for a fixed time.
In this process, multiple points collective processing (hereinafter referred to as a “microlens system”) has been known in which a laser beam is branched into a multitude of beams by using a microlens array, and is condensed on a surface to be processed, by which many holes are formed in the subject to be processed.
When processing is performed by the aforementioned microlens system, a disadvantage that the laser beams are generally uneven at the early stage or when time has elapsed has been known.
Also, in order to perform laser processing precisely, mask projection processing has conventionally been known. The mask projection processing is a technique for performing processing by projecting a mask pattern on the surface to be processed by using a projection optical system.
In this technique, to decrease unevenness of processing, a beam homogenizer using a fly's eye integrator as shown in FIG. 19 has been used widely as a fixed type uniform illumination optical system.
In addition, a processing uniformizing technique using mechanical scan of beams has been known (for example, refer to Patent Documents 1 to 4).
Patent Document 1 describes a technique in which in the projection processing of an aperture, irradiation beam scanning to the aperture is performed by a moving mirror, by which the depth of processed bottom surface of single hole is uniformized.    Patent Documents 1: Japanese Patent No. 3199124
Patent Document 2 describes a technique in which in the projection processing of pattern mask, the pattern mask and a subject to be processed are moved in association with respect to irradiation beams, by which the processing depth is uniformized.    Patent Documents 2: Japanese Patent No. 3211206
Patent Document 3 describes a technique in which in the projection processing of an aperture, a scan system of parallel beams is formed in combination with an angularly movable mirror and a cylindrical lens, and irradiation beam scanning to the aperture is performed, by which the processing accuracy is uniformized.    Patent Documents 3: Japanese Unexamined Patent Application Publication No. 7-51878
Patent Document 4 describes a technique in which in the microlens system, in an example aiming at the performance of processing in a wide range, unevenness of irradiation can be decreased by beam scanning in an area to be processed.    Patent Documents 4: Japanese Unexamined Patent Application Publication No. 2001-269789